Harmful Herpes, Helpful Herpes

Viruses can protect you from bacterial diseases.

Earlier this year, virologists showed that infection with cer­tain herpes simplex viruses might be linked to Alzheimer’s. Now they have some good news about the herpes virus family: Ironically named viral immunologist Herbert Virgin from Washington University School of Medicine has come up with some pretty convincing evidence that infection with two other members of the herpes virus family—the Epstein-Barr virus, which causes mononucleosis, and the relatively harmless cytomegalovirus—can actually protect a person from a range of bacterial infections.

Virgin first infected mice with the rodent equivalent of these two herpes strains and then exposed them to two types of bacteria: Listeria monocytogenes, a common cause of food poisoning, and Yersinia pestis, which causes bubonic plague. Both bacterial infections were lethal for mice that hadn’t been infected with herpes or that had active herpes infections. But those mice that were in latent stages of infection—carrying the virus but exhibiting no symptoms—survived the bacterial infections. And if beating the Black Death wasn’t convincing enough of herpes-related protection, Virgin also found a decrease in live bacteria in tissue samples taken from the latent-stage mice.

How could that be? Virgin believes latent infections boost immune signaling, helping the body to better fight invading bacteria. “We should think of these viruses as symbiotic, rather than as parasites all the time,” Virgin says. “But I’m not recommending people go out and get herpes; we found no benefit from the herpes simplex virus, which causes cold sores and genital sores.”